This invention is in the field of sensing of biological signals and also includes electrical communication between implanted devices, and between these devices and their sensors and stimulators. The invention also relates to leads used especially during medical procedures that require the use of magnetic fields.
Implantable medical devices having sensing and stimulation capacities are currently used in treatment of a wide array of medical disorders including, for example, neurological and cardiac abnormalities. In order to implement sensing and stimulation the implanted devices normally have leads which permit electrical communication between the device and the distal tip of the lead at which sensing or stimulation occurs. The leads are often comprised of one or more wires (“filars”), which may be straight or braided. Alternatively, wires may be replaced or wrapped within a mesh which is metallic-based or metallic-coated. Regardless of design, while significant efforts have been made to deter post-implantation breakage within the implanted leads this still occurs due to bending, kinking, and repetitive stress forces which occur during normal activity by the patient. Further, while flexible, the current leads are not configured to allow stretching.
Known methods of addressing this problem include U.S. Pat. No. 7,065,411 to Verness entitled “Electrical medical leads employing conductive aerogel” (the '411 patent) which describes implementing a conductive aerogel and a metallic lead within an insulative sheath. An areogel is nanoscle mesoporous material, containing very little mass (e.g., 99.8% air and 0.2% matter). The '411 patent is a relatively high-tech solution which has culminated from failure of more basic approaches as is reviewed therein. For example, U.S. Pat. No. 5,007,43 describes coiled wire conductors that are parallel-wound and separately coupled between a proximal and distal connector. Similar prior art embodiments describe various embodiments such as leads comprising coiled wire lumens, multi-filar leads embedded in various types of sheaths, leads using both serial and parallel configurations, leads with stranded wires, and the like. The '530 application also describes other known strategies for increasing life and durability of leads, such as multiple concentric-lumen designs wherein an interior lumen houses the conductive filar, and provides mobility within an outer sheath when movement occurs. Further, concentric lumen and their respective components may be bathed in a liquid silicone fluid or other lubricating medium in order to deter the risk of tension and breakage. Additionally, the conductive filer may be fitted within a conductive silicone rubber tube to provide a redundant system which is able to compensate for fracture and reduced conductivity of the wire filar.
It is also known that leads which are either implanted or which are external to the patient and which contain metallic wire conductors may show unwanted characteristics when submitted to magnetic fields of the type that may be used during certain medical procedures. For example, during medical imaging procedures which use strong magnetic fields such as magnetic resonance imaging (MRI) procedures, including functional MRI (fMRI) procedures, wire-based leads may be prone to induced currents which cause unwanted side-effects, such as thermal or electrical generation, which are a large safety issue for the patient. These side-effects can be harmful to the patient and may also cause distortion of the data obtained during the imaging procedure. It would be preferable to avoid these unwanted side-effects.
Catheters, made of either conductive or non-conductive materials, have been investigated using catheters containing either saline or guidewires (Ream et al, 1977; Lipton et al 1978). These catheters were used for experimental purposes in order to investigate issues of patient safety related to cardiac catheterization, and in order to examine the risk of spurious fibrillation caused by leakage currents induced from external equipment. In these studies, the saline within the catheters was not used for sensing or stimulation, but rather for manipulation of the leakage currents.
In U.S. Pat. No. 6,620,159, entitled “conductive expandable electrode body and method of manufacturing the same”, to Hegde, there is described an ablation catheter which contains a ballooned electrode assembly. The catheter both transmits electrical energy and also establishes the radius of a balloon using an electroconductive fluid which is pumped into the balloon. The '159 patent describes a number advantages over U.S. Pat. No. 6,012,457, to Lesh, which, in turn, describes a similar device wherein the electroconductive fluid is further used as an interface between the catheter's distal tip and the surrounding tissue in order to transmit the electrical energy to surrounding tissue. In U.S. Pat. No. 6,529,778 entitled “Fluid-phase electrode lead” summarizes devices which provide fluid to the electrode-tissue interface and discloses a fluid-phase electrode which utilizes a vacuum to anchor the distal tip to the target tissue.
Saline filled glass electrodes are often used as micro-electrodes when recording intracellular activity and membrane dynamics using patch-clamp techniques and when regulating current or voltage using clamp techniques (e.g. Neher & Sakmann 1976). The goal of a voltage clamp experiment is to measure membrane current. To do this, one monitors the membrane voltage and injects current to attain and maintain the desired voltage: a voltage-clamp amplifier and electrode must be able to: 1) measure voltage and 2) pass current in order to regulate the cellular voltage Patch-clamp techniques allow cellular function and regulation to be studied at a molecular level by observing currents through individual ionic channels. The electrodes used in clamp-type experiments are never flexible or subjected to magnetic fields as would occur during an MRI procedure.
U.S. Pat. No. 6,591,143 describes a “bending sensor for an implantable lead.” The sensor has an electrical resistance that various depending on how much the sensor is bent. The variable resistance is effected by a sending a current through fluid filled cavities and comparing the voltage drop across different cavities.
U.S. Pat. No. 5,458,630, to Hoegnelid et al. describes a “medical electrode device having a non-gaseous fluid conductor”. The conductor employs a non-gaseous, non-metallic electro-conductive gel which transmits electrical signals along the length of the lead.